VvFT and VvMADS8, the grapevine homologues of the floral integrators FT and SOC1, have unique expression patterns in grapevine and hasten flowering in Arabidopsis

The Vitis vinifera L. flowering genes VvFT and VvMADS8 from the grapevine cultivar Cabernet Sauvignon have been isolated. Sequence analyses showed that VvFT and VvMADS8 were highly homologous to the floral integrators, FLOWERING LOCUS T (FT) and SUPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), respectively, from Arabidopsis. The expression pattern studied through real-time PCR revealed that expression of VvFT was quite low in axillary buds and high in developing inflorescence and berries. VvMADS8 was highly expressed in the axillary buds at the time when inflorescence primordia were being initiated in these buds suggesting that VvMADS8 is a gene involved in the early stages of inflorescence development. In tendrils, considered to be modified inflorescences, VvMADS8 was weakly expressed but high expression of VvFT in these organs showed that expression was irrespective of the flowering process. Through in situ hybridisation, strong expression of VvFT was detected in stamens and the ovary and ovule suggesting additional roles for VvFT in fruit and seed development. Strong expression of VvMADS8 was detected on the inflorescence primordium within the axillary bud. Overexpression of VvFT and VvMADS8 in Arabidopsis hastened flowering showing that both these genes function as promoters of flowering when ectopically expressed in a heterologous plant.